Writing apparatus for use with galvanometer devices

ABSTRACT

A stylus for use with a recording galvanometer instrument wherein desired stylus pressure on a writing surface is obtained by providing magnetic material in association with the stylus. The fringing magnetic flux field of the galvanometer attracts the magnetic material and the attractive force is transferred to the stylus to provide the desired stylus pressure.

United States Paten 11 1 1111 3,728,735

Burton [451 Apr. 17, 1973 1541 W I IN APPARATUS FOR USE WITH 3,346,871l0/l967 Fowler ..346/l39 c GALVANOMETER DEVICES 3,434,159 3/1969 Erdman..346/l39 C [75] Inventor: James A. Burton, Houston, Tex. primary E i jh w Hartary [73] Assigneez AMF Incorporaed Att0rneyGe0rge W. Price andJohn H. Gallagher [22] Filed: May 3, 1971 57 ABSTRACT [21] Appl. No.:139,405 A stylus for use with a recording galvanometer instrumentwherein desired stylus pressure on a writing sur- 52 U.S. c1. ..346/l39c, 324/151 R face is Obtained y providing magnetic material in 51 Int.Cl. ..G0ld 15/24 sociatioh with the y The fringing magnetic flux 58Field of Search ..346/1 39 c, 139 R; field of the galvanometer attractsthe magnetic materi- 324/151 R al and the attractive force istransferred to the stylus to provide the desired stylus pressure. [56]References Cited 9 Claims, 3 Drawing Figures UNITED STATES PATENTS2,955,895 10/1960 Buoymaster et al. ..346/l39 C X 50 4o INK t SUPPLY 48J 47 N I r E 49 f4 E 26 U 1 CK 0 f6 ZO z; 2 15 1 12 i t .1

PATENTEDAPR 1 Y m INK SUPPLY FIGVI INI ENTOR.

JA MES A. BURTON ATTORNEY WRITING APPARATUS FOR USE WITH GALVANOMETERDEVICES BACKGROUND OF THE INVENTION In the art of electricalmeasurements, an instrument called a strip chart recorder is widely usedto provide a permanent visual record of a measured quantity orcharacteristic. As is well known, this type of recorder includes aDArsonval instrument, or galvanometer, which is comprised of a generallyrectangularly shaped electrical coil disposed between the poles of apermanent magnet. The coil is free to rotate in the magnetic field ofthe permanent magnet and a stylus for making a trace on a moving writingsurface such as a strip of paper is secured to and movable with thecoil. Current whose characteristic is to be recorded is coupled to thecoil and causes the coil to rotate or pivot as a function of the currentpassing therethrough. In many strip chart recorders the stylus is a thintube which is connected to a reservoir of ink, thus functioning as a pento produce an ink trace on a sheet of paper which moves relative to thepen. To obtain a good legible trace on the paper the stylus must contactthe paper with a pressure which is supplied by any of various types ofspring arrangements associated with the stylus and the apparatus forattaching the stylus to the deflection coil of the DArsonval instrument.Usually, the pen, the apparatus for mounting the pen on the coil, andthe spring arrangement are rather delicate and small in size, thusrequiring careful use and handling to assure proper functioning of therecorder. Proper and uniform pressure of the stylus on the writingsurface is required to achieve uniform and accurate response from theDArsonval instrument and to assure that the stylus will produce alegible and uniform trace on the writing surface. If the pen pressure istoo great, the pen will be restrained in its movement so that it cannotproperly respond to the high frequency signals from the DArsonvalinstrument, and if the pen pressure is too light the pen willoverrespond to short duration high frequency signals thereby producingdistorted spikes on the paper and flinging ink over the surface of thepaper.

In the use of strip chart pen recorders the flow of ink through thestylus often is impeded either because the ink dries in the stylus orbecause foreign substance blocks the flow of ink. When this occurs theoperator of the equipment must remove the stylus and correct thetrouble. Because of the delicate nature of the instrument, the stylus,the spring arrangement, and the mechanism for connecting the stylus tothe deflection coil all are subject to bending, distortion,misalignment, or other types of damage which may affect the functioningof the galvanometer and/or the pressure of the stylus on the writingsurface. When the instrumentsare used in the field" where they arelikely to be subjected to a vigorous physical environment includingshock, viration, dust, etc., the above-mentioned difficulties areexperienced to a considerable extent. The more frequently the equipmentoperator must handle and make adjustments to the delicate apparatus themore likely it is that further malfunction or damage may occur.Additonally, considerable time is lost when the operator becomesinvolved in making the adjustments and repairs discussed above.

BRIEF SUMMARY OF THE INVENTION The invention is a simple and reliablearrangement for achieving desired and unchanging pressure of a writingstylus of a recording galvanometer on the writing surface. The stylus ismounted on the galvanometer substantially free of any restraint on itsmovement about a horizontal axis, and without any mechanical arrangementfor applying a force to provide pressure of the writing end of thestylus on the writing surface.

Because the galvanometer includes a permanent magnet which has ratherlarge magnetic poles, a fringing magnetic flux field extends outwardlyfrom the poles to the exterior portion of the instrument. This fringingfield is fixed in position and, for practical purposes, may beconsidered to be unchanging in magnitude.

Magnetic material is provided as part of, or as an adjunct to the stylusstructure and is located so as to be in the fringing field of thepermanent magnet of the D'Arsonval instrument. The fringing magneticfield exerts a constant attractive force on the magnetic material in thestylus and maintains a constant pressure of the stylus on the writingsurface. No springs or other types of mechanical arrangements arerequired so that when replacement or repair of the stylus is requiredthere is little likelihood that any change in stylus pressure willoccur. Additionally, a simple arrangement may be used for attaching thestylus to the galvanometer instrument.

BRIEF DESCRIPTION OF DRAWINGS bodiment of a pen stylus constructed inaccordance with the principle of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, theDArsonval instrument, or galvanometer, 10 is shown in simplified formsince these types of instruments are well known in the art and the basicinstrument itself is not the subject of this invention. The instrumentis comprised of a horseshoe permanent magnet 12 having the pole pieces13 and 14. The faces of pole pieces 13 and 14 are curved to provide aradially directed magnetic flux field 15 that extends between the facesof the pole pieces. Magnetic flux field 15 is substantially uniformlydistributed in the region between the pole pieces 13 and 14 and, forpractical purposes, is constant in magnitude.

An electrical coil 16 having a plurality of turns is disposed in themagnetic field between pole pieces 13 and 14. Coil 16 is the currentresponsive element of the instrument and is rotatably supported relativeto the frame of the instrument (not illustrated) by suitable means 20and 21 which may be any of several known means such as jewelled bearingsand an appropriate spring restraint. Electrical leads 24 and 25 connectcoil 16 to a transducer or other type of circuitry which provides theelectrical signal whose characteristic is to be monitored. Coil 16 willrotate in its bearings about a vertical axis through an angle that is afunction of the current passing therethrough.

Secured to the top of coil 16 and movable therewith is a supportingsocket 28 which receives therein a stylus support member 30 that is bestseen in FIG. 2. Stylus support member 30 is generally block shaped andhas a stud at its lower end which fits within socket 28 and is securedtherein as by a set screw (not illustrated) so that support member 30rotates with coil 16 and socket 28. The upper portion of stylus supportmember 30 is notch shaped and includes an open bore 32 which isaccessible from the top surface by means of the inclined surfaces 36 and37 of the notch.

Seated on top of support member 30 is a cap-like stylus retaining member40 having the side skirts 41 and 42 which fit over the sides of supportmember 30 in a manner so as not to act as clips or clamps, but yet witha minimum of clearance so that the cap 40 will not substantially wobbleor move about a vertical axis relative to the support member 30. Arocker pin 45 extends between side skirts 41 and 42 of cap 40 and issecured thereto. Rocker pin 45 is of smaller diameter than open bore 32and is received therein. Cap 40 is free to pivot on rocker pin 45relative to support member 30.

A tubular pen stylus 48 of conventional construction is secured to skirt41 of cap 40 and is movable therewith. The right end of stylus 48 isconnected by suitable means such as flexible tubing to an ink supply andthe left end of stylus 48 contacts the writing surface 49 which may be apaper strip chart. Styluses such as illustrated at 48 are commerciallyavailable, or may be fashioned from small metal tubing commonly used forhypodermic needles, for example. The materials used in styluses arerelatively noncorrosive metal such as stainless steel to minimizeclogging of the small capillary tube of the stylus due to chemicalaction of the ink with the metal. The metals used for the styluses arenonmagnetic.

In accordance with this invention a rigid supporting strut 50 of amagnetic material is secured at its right end to skirt 42 of cap 40 andis secured at its left end to stylus 48. In addition to functioning as amechanical stiffening member for stylus 48, strut 50 also functions toprovide means for holding stylus 48 on writing surface 49 with thedesired constant pressure. As seen in FIG. 1, the magnetic flux fieldbetween pole pieces 13 and 14 inherently fringes outwardly above andbetween the top surfaces of the pole pieces. Strut 50 is located in thisfringing magnetic field, and being a magnetic material, is attracteddownwardly by the attractive force of the fringing field. Thisattractive force exerted on strut 50 is transferred to stylus 48 sincethe strut is rigidly secured to stylus 48. Stylus 48, by virtue of itsattachment to cap 40, freely pivots about rocker pin 45 and contactswriting surface 49 with a pressure which is a function of the strengthof the fringing magnetic field and of the physical and magneticproperties of strut 50. The desired magnitude of stylus pressure isobtained by empirically selecting the proper size, location and magneticmaterial for strut 50.

Because strut 50 is fixed in position relative to stylus 48, and becausethe fringing magnetic field is unchanging in magnitude, the forceapplied to stylus 48 will be substantially constant. A particularlyattractive feature of this invention is that the fringing magnetic fieldalready exists in the galvanometer instrument so that no separate oradditional magnetic source need be provided. Additionally, no springs orclips are used so that there are no mechanical force applying meanswhich can get out of adjustment or become damaged. The very simplearrangement for attaching cap to support member 30 permits simple andrapid removal of the stylus for repair or replacement. After replacementof cap 40 the stylus pressure inherently will be the same magnitude asbefore. It is to be noted that the attractive force of the fringingmagnetic field on strut 50 also serves to hold rocker pin in bore 32.Because rocker pin 45 should be free to pivot in bore 32, cap 40 rockerpin 45, and possibly support member 30 should be made of a nonmagneticmaterial to avoid magnetic attraction therebetween and resulting bindingat the pivot formed by rocker pin 45 and bore 32.

An alternative embodiment of the present invention is illustrated insimplified form in FIG. 3 .wherein the magnetic strut of FIGS. 1 and 2is not utilized, but instead a thin sleeve of magnetic material isplaced on the stylus 48 and fixed in position by means of a set screw56. Sleeve 55 is located in the fringing magnetic field of pole pieces13 and 14 and its position on stylus 48 is chosen to obtain the magneticattractive force that produces the desired stylus pressure on thewriting surface 49. The construction of cap 40 and its attachment tostylus support member 30 will be the same as illustrated in FIGS. 1 and2. For mechanical reasons it may be desired to have some support forstylus 48 of FIG. 3. This may be provided in any manner desired.

It is to be understood that the writing implement that is movable withcoil 16 need not be the long hollow tube through which ink flows, asillustrated in FIGS. 1-3. The stylus arm may have at its end a ballpoint pen, or a graphite point, or some other type of writing implementmay be employed. Irrespective of the form of the writing implement, adesired pressure of that implement on a writing surface may be obtainedby providing a magnetic material in association with the implement,wherein the material is disposed in the fringing magnetic flux field ofthe galvanometer pole pieces.

In view of the above discussion, other embodiments operating inaccordance with the principle of this invention will become apparent tothose skilled in the art.

What is claimed is:

1. In a recording instrument having a movable response element disposedbetween magnetic pole pieces, wherein the pole pieces establish amagnetic flux field which intersects the element and also establish afringing magnetic flux field that extends outwardly beyond the polepieces, said instrument also having a writing implement mounted formovement with said element and located at least partially in or adjacentsaid fringing magnetic flux field, the improve ment in means forapplying a force to said writing implement to produce a desiredimplement pressure on a writing surface, said improvement comprisingmagnetic material associated with the implement and movable therewithand disposed in said fringing magnetic flux field, whereby the forceproduced by the fringing magnetic flux field acting on the magneticmaterial produces the desired implement pressure on the writing surface.

2. In a recording instrument having a movable response element disposedbetween magnetic pole pieces, wherein the pole pieces establish amagnetic flux field which intersects said element and a fringingmagnetic flux field that extends outwardly beyond the pole pieces, saidinstrument also having a stylus mounted for movement with said elementand located in or adjacent said fringing magnetic flux field, theimprovement in means for applying a force to said stylus to obtaindesired stylus pressure on a writing surface, said improvementcomprising a member of magnetic material coupled to and movable withsaid stylus and located in said fringing magnetic flux field, wherebythe force produced by the fringing magnetic flux field acting on themagnetic member is transferred to said stylus to apply the desiredstylus pressure on said writing surface. 3. In a recording instrumenthaving a movable response element disposed between magnetic pole pieces,wherein the pole pieces establish a magneticflux field which intersectssaid element and establish a fringing magnetic flux field that extendsoutwardly beyond the pole pieces, said instrument also having a writingstylus mounted for movement with said element about a first axis and forpivotal movement about a second axis transverse to said first axis, thestylus being located in or adjacent said fringing magnetic flux fieldand having its writing end adapted to engage a writing surface, theimprovement in means for applying a force to said stylus to obtaindesired pressure of its writing end on a writing surface, saidimprovement comprising a member of magnetic material attached to saidstylus and movable therewith, the member of mag netic material beinglocated in said fringing magnetic flux field, whereby the fringingmagnetic flux field attracts the magnetic member to apply to the stylusa force which acts about said second axis to produce desired styluspressure on the writing surface. 4. The improvement claimed in claim 3wherein the mounting of the stylus for pivotal movement about the secondaxis is accomplished by means comprised of a stylus support membersecured to and movable with said movable response element,

said support member having an end opposite said response elementprovided with a notch,

a .stylus retaining member having a pivot means disposed within saidnotch for pivotal movement therewith about said second axis,

said stylus being secured to said stylus retaining member and extendingtherefrom.

5. The improvement claimed in claim 4 wherein said member of magneticmaterial comprises an elongated strut secured at one end to said stylusretaining member and secured at its opposite end to said stylus.

6. The improvement in claim 4 wherein said member of magnetic materialis a sleeve positioned about said stylus.

7. A stylus for use in a recording instrument having a I movableresponsive element and magnetic pole pieces that produce a fringingmagnetic flux field thereabout, said stylus comprising an elongatedmember adapted to be coupled at one end to the responsive element andwhen so coupled being disposed at least partially in said fringingmagnetic flux field,

a member of magnetic material attached to said elongated member at aregion intermediate its two ends and movable with the elongated member,

said magnetic member being positioned on the elongated member forlocation in said fringing magnetic flux field.

8. The stylus claimed in claim 7 wherein said member of magneticmaterial surrounds said elongated member.

9. The stylus claimed in claim 7 wherein said member of magneticmaterial is an elongated strut adapted for supporting said elongatedmember.

1. In a recording instrument having a movable response element disposedbetween magnetic pole pieces, wherein the pole pieces establish amagnetic flux field which intersects the element and also establish afringing magnetic flux field that extends outwardly beyond the polepieces, said instrument also having a writing implement mounted formovement with said element and located at least partially in or adjacentsaid fringing magnetic flux field, the improvement in means for applyinga force to said writing implement to produce a desired implementpressure on a writing surface, said improvement comprising magneticmaterial associated with the implement and movable therewith anddisposed in said fringing magnetic flux field, whereby the forceproduced by the fringing magnetic flux field acting on the magneticmaterial produces the desired implement pressure on the writing surface.2. In a recording instrument having a movable response element disposedbetween magnetic pole pieces, wherein the pole pieces establish amagnetic flux field which intersects said element and a fringingmagnetic flux field that extends outwardly beyond the pole pieces, saidinstrument also having a stylus mounted for movement with said elementand located in or adjacent said fringing magnetic flux field, theimprovement in means for applying a force to said stylus to obtaindesired stylus pressure on a writing surface, said improvementcomprising a member of magnetic material coupled to and movable withsaid stylus and located in said fringing magnetic flux field, wherebythe force produced by the fringing magnetic flux field acting on themagnetic member is transferred to said stylus to apply the desiredstylus pressure on said writing surface.
 3. In a recording instrumenthaving a movable response element disposed between magnetic pole pieces,wherein the pole pieces establish a magnetic flux field which intersectssaid element and establish a fringing magnetic flux field that extendsoutwardly beyond the pole pieces, said instrument also having a writingstylus mounted for movement with said element about a first axis and forpivotal movement about a second axis transverse to said first axis, thestylus being located in or adjacent said fringing magnetic flux fieldand having its writing end adapted to engage a writing surface, theimprovement in means for applying a force to said stylus to obtaindesired pressure of its writing end on a writing surface, saidimprovement comprising a member of magnetic material attached to saidstylus and movable therewith, the member of magnetic material beinglocated in said fringing magnetic flux field, whereby the fringingmagnetic flux field attracts the magnetic member to apply to the Stylusa force which acts about said second axis to produce desired styluspressure on the writing surface.
 4. The improvement claimed in claim 3wherein the mounting of the stylus for pivotal movement about the secondaxis is accomplished by means comprised of a stylus support membersecured to and movable with said movable response element, said supportmember having an end opposite said response element provided with anotch, a stylus retaining member having a pivot means disposed withinsaid notch for pivotal movement therewith about said second axis, saidstylus being secured to said stylus retaining member and extendingtherefrom.
 5. The improvement claimed in claim 4 wherein said member ofmagnetic material comprises an elongated strut secured at one end tosaid stylus retaining member and secured at its opposite end to saidstylus.
 6. The improvement in claim 4 wherein said member of magneticmaterial is a sleeve positioned about said stylus.
 7. A stylus for usein a recording instrument having a movable responsive element andmagnetic pole pieces that produce a fringing magnetic flux fieldthereabout, said stylus comprising an elongated member adapted to becoupled at one end to the responsive element and when so coupled beingdisposed at least partially in said fringing magnetic flux field, amember of magnetic material attached to said elongated member at aregion intermediate its two ends and movable with the elongated member,said magnetic member being positioned on the elongated member forlocation in said fringing magnetic flux field.
 8. The stylus claimed inclaim 7 wherein said member of magnetic material surrounds saidelongated member.
 9. The stylus claimed in claim 7 wherein said memberof magnetic material is an elongated strut adapted for supporting saidelongated member.